1. Field of the Invention
The subject invention relates to a blunt cannula with a filter material disposed therein for separating constituent parts of a bodily fluid, such as blood. The invention also relates to a kit of parts that includes a point-of-care testing cartridge and a blunt cannula that has an internal filter and to a method of using such a blunt cannula and filter with a point-of-care testing cartridge.
2. Description of the Related Art
Many medical procedures require diagnostic tests to be performed on a sample of bodily fluid. Some such tests require the bodily fluid to be separated into its constituent parts. For example, plasma is the fluid part of blood. Some diagnostic tests require the plasma, with its clotting mechanisms in tact, to be separated from more solid components of blood.
The prior art includes arrangements of glass fibers within instrumentation and filter devices for separating plasma from blood. Such systems are shown, for example, in U.S. Pat. No. 4,619,639, U.S. Pat. No. 4,810,394 and U.S. Pat. No. 5,460,777. Other materials are used for filtration in blood bags, test strips, card analysis systems and in-line filter systems.
Blood and other bodily fluids typically are analyzed in a laboratory remote from the patient. However, point-of-care testing systems have been developed recently. The prior art point-of-care testing system includes a portable clinical analyzer and testing cartridges. The testing cartridge comprises a small housing with an internal reservoir for receiving a small volume of blood, typically in the range of 65 μl and 110 μl. The testing cartridge further includes an inlet port that communicates with the internal reservoir and a plurality of contact pads and sensors. Blood can be collected in a conventional prior art syringe and then injected from the syringe into the inlet port of the testing cartridge. The contact pads and sensors of the testing cartridge then are engaged in a receptacle of the portable clinical analyzer. The analyzer performs certain diagnostic tests and provides a point-of-care read out of the test results. The portable clinical analyzer can be used with a printer to provide a printed output and with an interface to provide communication with a central data station that will store and appropriately utilize the test results. Examples of point-of-care test systems, as described above, are provided by i-STAT Corporation, Diametrics Medical, Inc. and AVL Scientific Corporation.
Point-of-care testing cartridges primarily receive anti-coagulated whole blood for analysis. This may require the cartridge to separate the cellular components of blood, as in the Abbott Vision System. Alternatively, the cartridge may use sensors for direct measurement of the analytes, such as in the Abbott i-STAT system.
Point-of-care testing systems offer many efficiencies over laboratory analysis. However, it is difficult to transfer blood accurately from the syringe to the testing cartridge. More particularly, it is unsafe and/or undesirable to use a contaminated sharply pointed metallic needle cannula while manipulating the very small testing cartridge. Thus, it is preferable to manually disengage the used needle cannula from the syringe. The user then must attempt to guide the short and relatively wide Luer tip of the syringe to the small inlet port of the testing cartridge. Significant risk exists for missing the inlet port and losing at least a portion of the blood that had been collected. This stray blood creates the risk for contamination and may leave an insufficient volume of blood to complete the diagnostic tests. Thus, the healthcare technician may have to perform another inconvenient and painful drawing of blood from the patient. Furthermore, the partly filled testing cartridge may have to be discarded, thereby increasing costs associated with a fairly simple diagnostic test.
Plastic cannulas are a suitable substitute for sharply pointed metallic cannulas in many situations, including those situations where a cannula must pierce a septum or where a connection with an IV fitting is appropriate. The prior art plastic cannula is unitarily molded from plastic and includes a proximal end, a distal end and a lumen extending between the ends. The lumen is widely open and tapered at the proximal end of the plastic cannula and is configured for fluid-tight frictional engagement over the tapered tip of a typical Luer fitting. The proximal end of a plastic cannula may further includes diametrically opposite projections that are dimensioned and configured for engagement with the threads of a Luer collar.
The distal end of the prior art plastic cannula includes a narrow cylindrical wall that surrounds the lumen through the cannula. The narrow cylindrical wall may be conically tapered to define a fairly blunt tip. However, some prior art plastic cannulas have a distal tip that is sufficiently sharp to pierce a rubber septum. In this regard, the sharpness of the distal tip normally would be limited by the diameter of the lumen through the cannula. This would result in a fairly blunt tip that might not be able to pierce through many septums. However, plastic cannulas have been developed with diametrically opposite triangular extension of the tubular sidewall at the extreme distal end of the plastic cannula. These triangular extensions converge and meet at a well defined point at the extreme distal end of the plastic cannula. A pair of identical side ports open transversely at the distal end and at locations between these converging triangular extensions. A plastic cannula of this type often is used to deliver a drug intravenously through the septum on an IV fitting. Although the blunt cannula is sufficiently sharp to pierce a septum, it will not accidentally stick a patient.
It is an object of the subject invention to provide a convenient way for separating plasma from blood and efficiently delivering the plasma to a point-of-care testing cartridge for analysis.